This invention relates generally to improvements in a filter-drier unit for use in the liquid line of reverse-cycle refrigeration and air-conditioning systems, more commonly known as heat pumps.
Filter-driers have been used in the conventional refrigeration and air-conditioning systems which only have flow in one direction. Therefore, the screens and filtering media of these filter-driers are normally at the outlet end to collect not only dirt from the system but to prevent any possible desiccant migration out of the outlet end of the filter-drier.
Screens or other filtering media at the inlet of such heretofore conventional filter-driers are sometimes used, but are not required. When such screens or other filter media are used, they are used primarily to retain the desiccant. Usually, the inlet portion of these filter-driers is not suitable for installing any type of screen or filter media because the filtering area is very small. Consequently, any dirt from the system would rapidly plug up the small filtering area of the screen. Therefore, such filter-driers usually avoid the use of a small area screen at the inlet end because it will rapidly plug up.
If these heretofore conventional filter-driers are used in heat pump systems in which there is a reverse flow or draining of liquid refrigerant out of the inlet fitting of the filter-drier, some crushed desiccant particles in the desiccant bed will be washed out of the inlet fitting and into the expansion device of the system, thereby causing a likelihood of blockage of the refrigerant flow.